The invention relates to a chucking device, in particular for workpieces that are to be machined on more than one side, having a workpiece carrier; at least one turret or workpiece holding table, arranged to receive workpieces, which is supported, rotatably about an axis of rotation, on the workpiece carrier; and a positive-engagement locking device, associated with the turret, on the workpiece carrier, by which locking device the turret can be locked positionally precisely in a predetermined rotary angle position relative to the workpiece carrier.
From U.S. Pat. No. 6,185,802, a multiple chucking device for workpieces to be machined on more than one side is known, which has an elongated workpiece carrier of polygonal cross section that has at least two chucking faces extending parallel to its central longitudinal axis, and which on at least one side is rotatably supported about its longitudinal axis by 360xc2x0 in stationary bearing means. At least two turrets are disposed side by side in a row on each of its chucking faces. All the turrets are coupled by positive engagement by gear means to one another and to a common drive source, in such a way that as a function of a rotary motion of the workpiece carrier about its central longitudinal axis, all the turrets are rotated about their respective axes of rotation by a predetermined angular value that is dependent on the rotation of the workpiece carrier.
Each of the turrets is assigned a positive-engagement locking device on the workpiece carrier, by which locking device the turret and thus the workpiece clamped to it can be locked positionally correctly in a predetermined rotary angle position relative to the workpiece carrier. To that end, the locking device has two annular locking parts, coaxial to one another, which each carry one serration, as a locking means, on the plane faces facing one another, and of which a first locking part is bolted to the turret, and the second locking part is connected to the workpiece carrier in a manner fixed against relative rotation. By means of actuating means with a pressure-medium-actuated reciprocating cylinder (hydraulic cylinder), the two serrations can be brought out of engagement, so that the turrets coupled by positive engagement to a common drive source via gear means can be adjusted, each by the same angle of rotation about its central longitudinal axis, as a function of a rotary motion of the workpiece carrier. After a new rotary angle position has been set, the serrations of the two locking parts are brought back into engagement with one another, so that for the ensuing machining of the workpieces clamped to them, the turrets are locked exactly positionally correctly and rigidly against the workpiece carrier.
The advantage of this embodiment of the turrets with locking parts that carry serrations is that the serrations assure optimal indexing precision and centering. Thus during the workpiece machining, close-tolerance, exact positioning of each turret exists relative to the workpiece carrier, and the connection between the turret and the workpiece carrier allows high force to be transmitted and at the same time offers high precision. At the same time, stringent demands for precision are made of neither the drive device, which when the gears are out of engagement with one another puts each of the turrets into a new position relative to the workpiece carrier, or in other words executes an indexing operation, nor the elements of the drive device that generate the rotary motion. It suffices for the drive device to bring the respective turret close enough to the desired angular position that the two gears mesh positionally correctly with one another upon the locking of the turret.
To assure the precisely positionally correct mutual engagement of the gears upon locking of the turrets that have been rotated approximately to a new angular position, a tooth size or tooth pitch of the gears is required that with certainty allows the existing angular position tolerances in the rotary motion of the turrets to be compensated for. With this condition, the maximum possible number of teeth in the gears is limited; that is, the tooth pitch must not fall below a minimum value that is dependent on the dimensions of the locking parts. As a result, angular pitches of less than approximately 1xc2x0 are hardly feasible in practical terms. However, there are instances in machining in which the workpieces clamped to the turrets must be rotated, between machining operations, by angular values that are less than 1xc2x0, for instance.
From U.S. Pat. No. 3,846,912, an indexing mechanism is known, which has a plurality of indexing disks disposed coaxially to one another that have gears with different tooth pitches, which can be brought selectively into and out of engagement by axial relative motions of the indexing disks. Thus a workpiece disposed on one of the disks can be rotated by very small angular increments about the disk axis on the vernier principle, and locked by positive engagement, exactly positionally correctly, in the particular angular position desired. The patent does not disclose any constructional details of an indexing device for which this indexing mechanism could be used.
An incremental rotation and fixation of a chucking plate, supported in a housing rotatably about its center axis is permitted by a round indexing table described in German Patent Disclosures DE-A1 32 09 519 and DE-A1 32 39 556. This round indexing table has a positive-engagement locking device, with four pairs of cooperating gear rings, of which two ring gears, located in the same plane, are embodied on an annular piston that is supported rotatably and axially displaceably in the housing, coaxially to the chucking plate. By a suitable axial displacement of the annular piston, its two gear rings can be brought into and out of engagement with the gear rings associated with them, in order to lock the chucking plate exactly positionally correctly in the particular desired angular position against the housing, and unlock it in order to set a different angular position. While the indexing table does make it possible to achieve indexing increments by the vernier effect of fractions of degrees for the chucking plate, nevertheless to that end it requires two separate drive mechanisms for the chucking plate and for the annular piston. Both drive mechanisms must have their own control devices, so that they can each approach the particular desired angular position of the chucking plate. Indexing tables of this type are therefore complicated in construction, and because of their design and the requisite drive elements, they are unsuited to being built in large numbers into one common workpiece carrier, as is required in multiple chucking devices for simultaneously machining a plurality of identical workpieces.
It is one object of the present invention to create a chucking device of the type defined at the outset whose turret can be rotated by small incremental angular steps, in particular of less than 1xc2x0 each, and then positioned fixedly, without requiring additional positioning drive mechanisms and controls; the chucking device should be distinguished by a simple, space-saving design and thus allowing versatility in use.
For attaining this and other objects, one aspect of the present invention is directed to a chucking device having a work piece carrier and at least one turret, arranged to receive workpieces, which is supported, rotatably about an axis of rotation, on the workpiece carrier. A positive-engagement locking device on the workpiece carrier, associated with the at least one turret, has at least three locking parts coaxial to one another, of which a first locking part is solidly connected to the turret and a second locking part is solidly connected to the workpiece carrier, and at least one third locking part is disposed between the first locking part and the second locking part and is supported rotatably relative to the workpiece carrier, and all the locking parts, on faces facing one another, each carry pairs of cooperating locking means which can be brought into and out of engagement with one another by means of an axial relative motion of the locking parts. The chucking device also includes actuating means for bringing the locking means of the locking parts selectively into and out of engagement in such a way that the at least one third locking part, via its locking means, always remains positively locked with at least one locking part adjacent to it. A drive device, which is coupled to the turret, serves to rotate the turret by a predetermined angular value about its axis of rotation when the locking means are released.
Thus the turret can be put into a respective new desired angular position, in which it is subsequently positioned exactly positionally correctly by the provision that, by means of the actuating means, the locking means are brought by positive engagement into engagement with one another.
Various specific features can also be provided. For example, as a rule, each of the locking means has a crown gear, in particular a serration, but embodiments are also conceivable in which positive-engagement locking means in the form of suitably disposed prisms, perforated disks with indexing bolts, and so forth are used.
Also, the third locking part disposed between the first and second locking parts is advantageously embodied as an annular disk, which on both facing plane sides carries respective locking means, preferably in the form of a crown gear and in particular a serration. This third locking part is advantageously rotatably supported with radial play, or in other words with limited radial mobility between the first and second locking parts. This loose disposition of the third locking part assures that the gears associated with one another, which as a rule are embodied as gear rings, can upon entering into engagement with one another center one another unhindered and can mesh with one another, so that the high precision of positioning of the locking parts and thus of the turret remains assured. The intrinsically loosely supported third locking part, both in the lifting motion of the turret to undo its locking and in the ensuing rotary motion for shifting into a new angular position, always remains kept in engagement with either the first or the second locking part, and therefore it always has a controlled position, determined beforehand, relative to the turret or the workpiece carrier, as is necessary for the replicable setting of a predetermined rotary angle value for the position of the turret. The crown gear of the first locking part and the crown gear, associated with it, of the third locking part have a different tooth pitch from the crown gear of the second locking part and the crown gear, associated with it, of the third locking part. By a suitable choice of the tooth pitches (or of the pitches of the differently designed locking means), a very fine incremental rotary angle positioning of the turret can be performed, in which the rotary angle increments amount to merely fractions of 1xc2x0, as will be explained in further detail in the ensuing description of an exemplary embodiment.
Also, the novel chucking device can in principle be used as an indexing device or round indexing table with only one turret, but because of its simple, space-saving design and the fact that it requires only a single drive device for the turret and requires no additional drive and control devices for indexing disks and the like, it is especially suitable for use as well in the form of a multiple chucking device. To that end, the workpiece carrier can be designed as polygonal in cross section and can have at least two chucking faces, extending parallel to its longitudinal axis, with at least one turret disposed on each chucking face.
In a fundamentally similar embodiment to that described in U.S. Pat. No. 6,185,802, a multiple chucking device of this nature can have one common drive source for all the turrets of the drive device, with which source the gear means of the turrets are coupled by positive engagement, so that upon a rotation of the workpiece carrier about its central longitudinal axis, all the turrets disposed on the workpiece carrier are rotated simultaneously about their respective axes of rotation by the same angle of rotation, which is in a fixed relationship to the angle of rotation of the workpiece carrier about its central longitudinal axis. The invention thus makes it possible for the multiple chucking device known from U.S. Pat. No. 6,185,802 to be improved and refined by simple means, without changing the outside dimensions and without substantially increasing the expense for control or driving, in such a way that it permits incremental indexing motions of the turrets by fractions of degrees. This is attained without impairing the strength and loadability of the turrets or the workpiece carrier, or of other elements serving to support and move these parts.